| Purpose:Fracture healing is a complex biological repair process, which was determined by several biomechanical factors. Several neuropeptide, including calcitonin gene related peptide (CGRP) and substance P, plays an important role in the regulation of fracture healing. CGRP has pleiotropic effects on bone cells; both osteoclasts and osteoblasts have functional receptors for CGRP. Several studies showed that CGRP has a role in promoting fracture healing. However, the relationship between the biomechanical environments and expression of CGRP receptor in local fractured tissue was not clear. Therefore, the aim of the present study is to evaluate the express of CGRP receptor based on the stability or instability biomechanical environments.Methods:(1) A new modified apparatus was designed by Solidwork12.0software and tested on40male Sprague-Dawley rats. Left femoral shaft fractures were created in20rats closely, and were treated with intramedullary nail. Other20rats received open osteotomy on the left femoral shaft, and were immobilized by plate. Operative time and success ratio were calculated separately.(2) Femoral shaft fractures were created in40rats, and were treated with an intramedully nail of0.8mm diameter or1.0mm diameter. Rats were then sacrificed at1,2.5or8weeks. Fracture calluses were analyzed using X-ray, Micro-CT, histological and biomechanical methods.(3)64male Sprague-Dawley rats were divided into two groups randomly. Left femoral shaft fractures were created in all rats closely. The rats in thin nail group were treated with0.8mm intramedullary nail, while thick nail group with1mm intramedullary nail. Rats were then sacrificed at1,2,5or8weeks. The express of CGRP receptor was evaluated by immunohistochemical staining, Western blot and qPCR.Result:(1) A closed fracture model was established with the modified apparatus. The operative time in closed fracture group was shorter than open fracture group. The success ratio in closed fracture group was superior to fracture group.(2) The X-ray showed that there was not significant between the two groups at any time points. At1week, there was no significant difference in bone volume (BV), total volume (TV), BV/TV and biomechanical testing. At2weeks, TV was significantly greater in the thin nail group than in the thick nail group. However, BV, BV/TV and biomechanical testing of the thick nail group was significantly superior to the thin nail group. At5weeks, TV was also significantly greater in the thin nail group than in the thick nail group. BV and BV/TV was significantly greater in the thick nail group than in the thin nail group. There was no significant difference in biomechanical testing between the two groups. At8weeks, there was no significant difference between the two groups in BV, TV, BV/TV and biomechanical testing.(3) At1and2weeks, the mRNA and protein expression of CGRP receptor in thin nail group was statistically significant than in the thick nail group. However, there was no significance in mRNA and protein expression of CGRP receptor between the thin and thick group at5and8weeks.Conclusion:(1) The modified apparatus is simple to use and inexpensive to build. It has good repeatable and operable feature, which could be used in the study for fracture healing.(2) In the early phase, instability is unfavorable to fracture healing, which may be compensated for the greater callus volume. In the later phase, instability leads to better mineralization and callus maturity.(3) Biomechanical environment in callus have an effect on the expression of CGRP receptor. In the early phase of fracture healing, instability leads to more expression of CGRP receptor than in the stable condition. CGRP signaling may target the early phase of fracture healing... |
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